Combustor cans in a multiple can array may communicate acoustically with each other. Large pressure oscillations, also known as combustion dynamics, may result when heat release fluctuations couple with combustor can acoustic tones. At particular operating conditions, combustion dynamics at specific frequencies and with sufficient amplitudes, which are in-phase and coherent, may produce undesirable sympathetic vibrations in the turbine and/or other downstream components. Typically, this problem is managed by combustor tuning. Combustor tuning to protect the turbine buckets, however, may impose severe restrictions on the function and operability of the combustor.
Altering the frequency relationship between two or more combustors may reduce the coherence of the combustion system as a whole so as to diminish any combustor-to-combustor coupling. As used herein, coherence refers to the strength of the linear relationship between two (or more) dynamic signals, which is strongly influenced by the degree of frequency overlap between them. As the combustion dynamics frequency in one combustor is driven away from that of the other combustors, modal coupling of combustion dynamics may be reduced, which, in turn, may reduce the ability of the combustor tone to cause a vibratory response in downstream components.
There is thus a desire for improved systems and methods for coherence reduction between combustor components and turbine components without requiring combustor tuning and other types of conventional frequency avoidance techniques. Systems and methods that reduce the modal coupling of combustion dynamics by altering the frequency difference between two or more combustors would be useful for enhancing the thermodynamic efficiency of the combustors, protecting against accelerated wear, promoting flame stability, and/or reducing undesirable emissions over a wide range of operating levels, without detrimentally impacting the life of the downstream hot gas path components.